THE ROLE OF SIZE EFFECTS AND PHASE POLYMORPHOUS TRANSFORMATIONS IN COMPOSITE CERAMICS ON THERMAL INSULATION CHARACTERISTICS AND RESISTANCE TO EXTERNAL INFLUENCES

The paper examines the role of changes in grain morphology associated with the processes of phase polymorphic transformations in ZrO₂ with varying concentrations of the stabilizing dopant Y₂O₃ on changes in thermophysical parameters, as well as resistance to external influences caused by sudden changes in temperature, mechanical loads, and prolonged thermal heating. An assessment of phase transformations caused by a change in the concentration of the stabilizing dopant Y₂O₃ showed that at low concentrations, the dominant role in phase changes is caused by processes of the m – ZrO₂ → t – Zr(Y)O₂ type, while at dopant concentrations above 0.10 M, processes with the formation of the pyrochlore phase Y₂Zr₂O₇ dominate, the phase formation processes of which led to grain coarsening during sintering. According to the assessment of thermal insulation characteristics, it was established that the dominance of the pyrochlore Y₂Zr₂O₇ phase in the composition of composite ceramics leads to a decrease in the thermal conductivity of ceramics, as well as an increase in the efficiency of thermal insulation, both in the case of low temperatures and under prolonged exposure to high-temperature heating. An assessment of the resistance of ceramics to thermal shock processes associated with a sharp change in heating-cooling temperature showed that composite ceramics with a dominant pyrochlore phase in the composition have greater resistance to temperature changes due to maintaining stability to external influences and low thermal conductivity.

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